1. Field of the Invention
This invention relates to a bicycle with a speed change gear, and more particularly to a bicycle with a speed change gear suitable for increasing the degree of freedom of the design of a bicycle body frame.
2. Description of Background Art
A bicycle with a speed change gear which includes an internal speed change gear disposed coaxially with a crankshaft is known. For example, in a bicycle disclosed in the official gazette of Japanese Patent Laid-Open No. Hei 6-48368, a motor is connected to a changeover lever of a speed change gear disposed on a crankshaft such that the speed change gear is changed over by the motor.
The bicycle with a speed change gear described above has the following problems. First, since the outputting position of the speed change gear for transmitting treadling force to a rear wheel is limited to the position on the crankshaft or in the proximity of the crankshaft, the degree of freedom of the design of the bicycle body is limited. In this situation, a swing arm for supporting the rear wheel thereon is configured for rocking motion with respect to a main frame of the bicycle body, and a rocking shaft (swing arm pivot) and an output power shaft of the speed change gear (the output power shaft is hereinafter referred to as speed change gear shaft) are spaced away from each other. With this configuration, a chain is liable to oscillate by rocking motion of the swing arm (the fluttering or the rocking motion is great). In order to minimize this problem, the rocking shaft and the shaft of the speed change gear are preferably disposed as near as possible. Accordingly, if the outputting position of the speed change gear is limited to a position on the crankshaft, then the position of the rocking shaft is also limited, thus limiting the degree of freedom of the design of the position of the rocking shaft.
Further, if the speed change gear is disposed on the crankshaft, then the width (dimension in the leftward and rightward direction of the bicycle body) of the crankshaft is restricted by the width of the speed change gear. Therefore, the distance between left and right pedals is also limited.